The following references to and descriptions of prior proposals or products are not intended to be, and are not to be construed as, statements or admissions of common general knowledge in the art in Australia or elsewhere.
Methods of electrolytic chlorination for the purpose of sanitising water, in particular, swimming pool and spa water have been disclosed. However, this invention is also applicable to other water sanitizing processes, such as involving water towers for air conditioning, and particularly any other application that requires the addition of a halogen sanitizer, such as chlorine, chlorine dioxide or bromine. An eleotrolytic chlorine generator may involve the supply of low voltage DC power to an electrolytic cell. Chlorine (or chlorine dioxide) is generated in solution with the relevant salts dissolved in water. The water containing the solute may be passed through the cell for the purpose of sanitizing a body of water, such as a pool, spa or water tower.
It has been disclosed that by adding a specific amount of sodium chloride to the body of water and providing an electrolytic cell powered by a low voltage DC source in a filtration system, chlorine gas may be produced in the cell and dissolved into the feed water. This process can be used to effectively sanitize and treat the body of water. Although an adverse byproduct of this process is the production of hydrogen gas H2(g), under normal operating conditions the H2(g) flows with the feed water into the body of water and escapes safely into the atmosphere. However, in some circumstances the water flow conditions may not be normal and it is at these times that safety issues arise with respect to H2(g) containment. For example, a blocked suction line, closed valve(s), incorrect installation or a seized pump can effect a loss of water flow. It may also cause present safety devices to become ineffective, inoperable and/or redundant. In such circumstances, the cell may continue to produce H2(g) such that the volume of H2(g) contained in the system may reach dangerously explosive levels. The H2(g) may continue to be produced and fill not only the cell chamber but all the filtration system plumbing and receptacles. A large H2(g) reservoir may result leading to a potentially explosive situation.
Electrolytic cells have been disclosed in which the electrodes are positioned in between inlet and discharge ports of the cell with no provision to trap and contain hydrogen gas in the event of a water flow stoppage. These cells are plumbed horizontally or vertically and may use flow switches plumbed in series with the cell to detect a water flow fault condition. In such an arrangement, the flow switch may be designed to suspend power to the cell to minimise the potential a H2(g) build up.
The use of a flow switch may be considered a good primary safeguard against a loss of water flow. However, the use of a flow switch alone as a single safe guard against hydrogen gas build up has been found, in the inventor's experience, to be insufficient. A flow switch is a mechanical device and therefore has a potential for failure. In the event of a water flow stoppage, a flow switch failure could cause a massive hydrogen gas volume to accumulate in the plumbing and filtration equipment and therefore become hazardous. To the inventor's knowledge and belief, this one safety device, which the inventor believes should only be used as a primary measure, is the only safety feature relied upon by electrolytic chlorinators currently on the market.
Cells have been disclosed having separate flow switches or integral flow switches which operate at 90 degrees to the direction of flow. A cell may be installed without plumbing the cell in a gas loop and where the cell is at the uppermost portion of the loop. In such an installation, an integral flow switch or a separate flow switch may be installed but a failure of the flow switch to detect a water flow failure could lead to a hydrogen gas is build up.
Other manufacturers have used a non mechanical conductive electrode arrangement positioned at the top of a horizontal cell chamber. However, such methods detect only the presence of water and not the flow of water. It may therefore fail to detect a lack of flow of water if the cell is not installed in the horizontal position as generally specified in installation instructions. Moreover, incorrect installation may find the sensor positioned at the lower portion of the cell rendering it effectively redundant. Incorrect orientation of the cell chamber may cause the inherent physical gas loop to no longer contain hydrogen gas in the event of a flow fault. If both return and suction line valves are closed, the chlorinator cell will continue to operate. The inability of the hydrogen gas to displace the water in the cell may lead to a pressure increase in the plumbing system and eventually damage the plumbing and potentially cause injury.
Chlorine generators vary greatly in design both with regard to the operation of the power supply and cell design. Where a single polarity direct current (DC) voltage is applied to the cell electrodes, regular acid washing to dissolve the calcium deposit from the electrodes may be require. Where a DC voltage is applied to the electrode bundle and periodically reversed, the calcium scale deposit may be dissolved to effectively prevent calcium scale build up.
Reversing the polarity onto the electrode bundle to effectively keep the electrodes free of calcium scale has been disclosed. One electrode bundle design previously described involves two electrodes on opposing ends of the plurality of solid plate electrodes having opposing polarity's. When a sufficient DC voltage is applied to the two electrodes and sufficiently saline water is passed through to permit electrolysis, an opposing charge is induced onto the plate surface which is parallel and in closest proximity. The other surface of this same plate attains the opposing polarity and will induce an opposing charge onto the next opposing plate surface and so on.
The electrode bundle effectively conducts the current through the plurality of electrode plates and the reaction to produce chlorine gas on the anode faces of the plates occurs. This electrode bundle design described is a bi-polar design and is used because it is compact. A bi-polar cell may operate as a single polarity system where acid washing is periodically required or when a specialised electrode coating is used. Thus the polarity may be periodically reversed to achieve the self cleaning affect.
The efficiency of electrode bundles is compromised in three major ways:
(1) If the electrode bundle is poorly designed with insufficient physical barriers positioned onto the electrode bundle, the current leakage may be excessive and this compromises efficiency.
(2) If the power supply is poorly designed and the DC voltage applied across the bundle is too low, the efficiency is reduced. Efficient cell designs have been disclosed, but their inability to operate at excessive salt levels without compromise to efficiency and electrode life mean that there is a need for a device which overcomes these difficulties. Manufacturer's salinity requirements vary but over salting of the body of water such as pool or spa water is a common problem. Where the salinity level in, for example, a pool or spa is up to 85% greater than that recommended, the chlorine production efficiency and electrode life time may decline.
Using a power supply with a larger amperage capacity allows the cell to draw a larger current under excess salt conditions. This prevents current limiting devices from prematurely reducing the voltage to the cell (which would otherwise cause the inefficiencies in the cell). However, the excess current drawn by the electrode will compromise the life time of the electrode and deliver more chlorine per hour than officially stated in technical or instruction manuals.
(3) If the salt level is higher than that required to operate the cell at 100% of the manufacturer's stated output, the increased cell load may cause the power supply to limit the current and, in effect, reduce the voltage delivered to the electrode bundle. This may cause the power supply to deliver a voltage of less than 4.0 volts per cell and the cell will produce chlorine inefficiently. It will also fail to clean itself effectively upon polarity reversal and cause excessive current leakage, thus reducing the life time of the electrode bundle.
It is an object of the present invention to ameliorate or overcome one or more of the disadvantages of the prior art or at least provide a useful alternative thereto.